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I think you need to seriously reconsider your strategy regarding monitoring your childrens use of the family PC.
Secretly monitoring use the way want to do it does nothing to engender trust or encourage responsible personal behaviors. It can also have the exact opposite effect on your relationship with your daughter.
The simple fact you want to install this software without her knowledge would seem to indicate your primary interest is in spying on her activities rather than dissuading her from what you fear she may be getting up to. This raises some ethical issues for me because the only two words I know that are used to describe the practice of covertly watching someone's activities are 'spying' and 'voyeurism.'
As a parent you have a responsibility to raise your child as best you are able. Secretly watching her internet usage is not a good way to accomplish that goal.
If you feel you need to do something to control web access, there are several so-called parental filters that can be used to block sites you may consider inappropriate for her to view. Far better, however, would be to have a a long and serious talk about what the rules are for Internet use in you home - and then let it be known that there are ways to monitor her PC but that you'd rather not feel you ever needed to take such a drastic measures.
If your goal is deterrence, that should be enough.
Note: Be very careful if you do install monitoring software despite what I've suggested. While the jury may be out on whether or not a parent can electronically monitor her child's activities, it's definitely not when it comes to monitoring somebody else's child as part of the process. So while you could claim a right to know what she's texting or file forwarding - you don't have a similiar claim on the responses she is getting in return. So even under the best circumstances, you only have a (debateable) 'legal right' to her half of the conversation. Since the other party has a "reasonable expectation of privacy" you're getting into some dangerous legal waters. Some parents have been prosecuted for this. The court didn't have a problem with them monitoring their own child. But they had a real big issue with a parent doing it to somebody else's child.
And when Internet usage is composed of something like 90% 'social use' in that age bracket, it's almost impossible not to spy on your own child without spying on somebody else's.